Measure Twice › Concrete
Concrete Calculator
Enter your slab size and thickness to get the number of bags of concrete, or how much ready-mix to order.
Worked example
- Slab length 10 ft
- Slab width 10 ft
- Thickness 4 in
- Bag size 30 kg bag
- Waste allowance 10%
Result:
- 30 kg bags
- 74 bags
- Concrete volume (incl. waste)
- 1.36 yd³
- Volume in cubic feet
- 36.7 ft³
- Ready-mix to order (rounded to ¼ m³)
- 1.25 m³
- Total weight of bags
- 2,220 kg
That's over 1 m³ (1.4 yd³). Ready-mix delivery is usually cheaper and far less work than 74 bags.
Load this example into the calculator
How the concrete calculator works
It multiplies length × width × thickness to get the volume, adds a waste allowance for uneven ground and spillage, then divides by the yield of one bag. A 30 kg bag of pre-mixed concrete makes roughly 0.014 m³ (about half a cubic foot), and other bag sizes scale with weight.
volume = length × width × thickness × (1 + waste %)
bags = volume ÷ yield per bag, rounded up
For a 10 × 10 ft slab, 4 in thick: 10 × 10 × (4 ÷ 12) = 33.3 ft³ = 0.94 m³ before waste.
Tips
- Check the yield on the bag. It’s printed on every bag and varies a little by brand and mix.
- Past about 1 m³, order ready-mix. That’s 70+ bags at 30 kg, which is a lot of mixing, and the truck usually works out cheaper. Many suppliers deliver in quarter-metre steps.
- Thickness: 4 in (10 cm) is typical for patios and walkways; driveways and shed pads that take heavier loads are usually thicker. Follow your project plans or local requirements.
- Base matters more than thickness. A compacted gravel base stops cracking and heaving through freeze-thaw cycles. The concrete patio calculator works out the base, excavation and rebar for you.
Where to buy in Metro Vancouver
Local suppliers we've checked. Nobody pays to be listed. Call ahead for prices, minimums and delivery to your area.
Ready-mix and small-load concrete
- Vancouver Ready Mix in Langley
Delivers across Metro Vancouver, with small loads and U-Cart concrete for pads and walkways.
- Yard At A Time Concrete in Delta
Mini trucks for tight residential sites; 1 yd³ minimum, up to about 2.4 m³ per load.
- Go Concrete in Surrey
Mixes on site, so you pay for what you pour. Serves the Lower Mainland.
Related calculators
- Concrete Patio Calculator
Replacing grass with concrete? Enter the slab size to get every layer, from how deep to dig to how much ready-mix to order.
- Concrete Driveway Calculator
Enter your driveway's size to get the excavation, gravel base, rebar and ready-mix you'll need.
- Fence Calculator
Enter your fence length and design to get posts, rails, pickets and the concrete to set the posts.
Last updated October 28, 2026